Washington County, Md has a wide range of water hardness. Extensive studies allow the categorization of enumeration districts by mean hardness, and private censuses done in 1963 and 1975 allow identification of persons at risk of dying of arteriosclerotic heart disease. Death rates will be calculated for various levels of hardness of drinking water, with adjustments for race, sex, age, smoking and socio-economic status. An investigation will also be made into the possible association of type of water pipes with arteriosclerotic heart disease.